Blind landing system



June 18, 1940. E. M. soRENsEN BLIND LANDING SYSTEM 4 Sheets-Sheet 1 Fild Jan. 28, 1938 n dz., w Z W a za? w w. z w., w J w W fa. w f w. E s C l/ vw w a V ,a ww WUFIM .m zi x w W a q Way m Am r a/ P /J ...MJ

June 18, 1940.

E. M. SORENSEN BLIND LANDING SYSTEM Filed Jan. 28, 1938 4 Sheets-Sheet 2 Radio Fecez'l/er` elecor Mec/zamsm June 18, 1940. E. M. soRENsEN 2.204.528

BLND LNDING SYSTEM Filed Jan. 28, 1988 4 snem-Sheet 3 June 189 E9 =1I` E. M soRENsx-:N

BLIND LANDING SYSTEM Filed Jan. 28, 1938 4 Sheets-Sheet 4 Patented June' 18, 1940 UNITED s'rA'rEs PA'I'ENTv OFFICE 14 Claims.

(Granted under the act of' March 3. 1883, as amended April 30, 1928; 370 0. G. 757) The invention descrlbed herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates broadly to a navigational guide for assisting a pilot in effecting avblind landing; more especially it is directed to a system and apparatus whereby under conditions of poor or of no visibility, the pilot of an aircraft, through the instrumentality of an automatically operated signal responsive apparatus aboard the aircraft will be informed regarding the position of the aircraft with reference to various marker and field receiver stations located adjacent to and within the boundaries of a landing field.

One object of this invention is to provide an improved aeronautical guide system and apparatus whereby the pilot of an aircraft, regardless of visibility conditions, may make a safe and accurate landing from any one of four approaches to a landing field, depending upon the direction of the prevailing wind, by heading the aircraft toward a selected area on the landing field, and shown on the screen of an automatically operated signal responsive indicator located aboard the aircraft and in front of the pilot.

Another object of this invention is to providea navigational aid for making blind landings wherein a rectangular field is laid out in squares. each including a field receiver station comprising a vertically disposed antenna connected with a receiver unit responsive to a predetermined frequency and housed in a subterrane'an compartment, and wherein each receiver unit controls a local audio oscillator Operating at a predetermined frequency and having its audio frequency output connected to a speech and signal transmitting unit common to all of the stations and located in a control tower positioned adjacent the landing field, whereby as the antenna systems of the various receiver units are impinged by radiations propagated by short wave transmitters located aboard the aircraft and transmitting at a frequency to which the receiver units are responsive, the output of the speech and signal transmitting unit will be modulated at difierent audio frequencies for the purpose of controlling the operation of a signal responsive position indicator located on the aircraft.

Another object of this, invention is to provide a system and apparatus of the character described wherein avpair of marker receiver stations responsive to a predetermined frequency are disposed in spaced relation along each of the lines bisecting the boundaries of a-rectangular landing field and wherein the landing field is divided into a series of equally dimensioned areas each of which contains a field receiver station tuned to a predetermined frequency and adapted 5 to control a local audio oscillator Operating at a predetermined frequency. the audio frequency output of the various oscillators 'being connected to a common field transmitting system whereby as 'the antenna systems of the various marker and receiver units are impingedV by radiations from short wave transmitters located aboard an aircraft and transmitted at frequencies to which the receiver and marker units are responsive, the output of the field transmitting system will be modulated at different audio frequencies for the purpose of controlling the operation of a signal responsive position indlcator located on the aircraft. i

Another object of this invention is to provide a system and apparatus of the character described .wherein an aircraft is provided with means for transmitting short wave radiations at different f-requencies in different directions, and with different radiation patterns, whereby depending upon the frequency of the short wave emanations, the direction of the propagation,

their pattern and the position of the aircraft relative' to the landing field, suitable signal responsive apparatus on the landing field will be controlled to effect modulation of the field transmitter output at different audio frequencies forthe Purpose of selectively illuminating various areas on a transparent facimile of the landing field and thereby informing the aircraft pilot regarding the position of the aircraft relative to the landing field and to a particular area on the field toward which the plane may be directed for a safe landing.

With these and other objects in view. this invention consists in certain novel details of construction, combination and arrangement of parts to be more partlcularly herelnafter described and claimed.

Although the novel features which are believed to be characteristic of this invention will be particularly pointed out in the claims appended hereto, the invention itself as to its objects and advantages, the mode of its operation and the manner of its organization may be better understood by. referring to the following description taken in connection with the accompanying drawings forming a part thereof in which Fig. 1 is a perspective view of the landing field, showing its layout, the 'arrangement of the elevation of the underground compartment used to house the short wave receiver unit, the local audio oscillator, the electro-magnetically controlled means for controlling the output of the' oscillator and the power supply, all of which are diagrammatically shown within the compartment;

Fig. 3 is a side elevation of an airplane showing the radiation pattern of one of the short wave beams adapted to be projected from the aircraft normal to its line of fiight and illustrating a fragment of the landing field and the area covered by the beam when the aircraft is at an altitude of 800 feet;

Fig. 4 is a front elevation of an airplane illus-' trating the radiation pattern of the marker control beam transmitted from the airplane, normal to its line of flight and illustrating the width of the beam at an altitude of 800 feet;

Fig. 5 is a side view of the airplane and beam shown in Fig. 4 and illustrating the breadth of the beam when the airplane is at an altitude of 800 feet;

Fig. 6 is a side elevation of an airplane showing the arrangement of the three short wave transmitters on the plane and the direction of. their transmitter beams;

Fig. 7 l,is a diagrammatic view of the three transmitter units, their modulator and'the switch for controlling the simultaneous operation of vthe assembly; I

Fig. 8 is" a perspective. view of the instrument board of an aircraft, showing the mounting of the position indicator, a compass, the remote con trol on the steering wheel for orienting the in-. dicator with respect Ato compassindications, and illustrating diagrammatically the selector mech-| anism casing and its connections with the out put of a conventional receiver;

Fig. 9 is a diagrammatic view of the landing field, the marker and receiver stations land the electrical connections between the marker and 'field receiver stations, the control panel and the' Fig. 11 is a transverse vertical section of the' position indicator and its casing, a portion of which is broken away and showing the manner of rotatably mounting the indicator within the casing, the means to the rear of the transparent panel of the indicator, lthe commutator rings for i supplying electrical energy to the illuminating h means, the brushes coacting with the commutator rings, and illustrating the electrical .connections between the brushes and certain of the electro-magnetically controlled switches of the selector mechanism;

Fig. 12 is a diagrammatic view illustri'ating the position indicator, 'the an'angement of its incandescent signal lamps, th'e electro-'magnetically controlled selector mechanism, the electrical connections between the selectormechanism'and megane the incandescent signal lamps of the indicator, and the conventional receiver, the audio output of which is connected with the selector mechanism; and

Fig. .13 is a transverse Vertical section taken on the line l3-I3 of Fig. 11, looking in the direction of the arrows.

For the sake of convenience and to simplify description, this invention will be discussed under the headings-Landing field arrangement and receiver stations; Landing field control tower-and transmitting equipment; Transmitter assembly aboard aircraft; Position indicator;v Selector mech'anism; Operation and concluslon. These components will be considered in the order of their enumeration.

anding field arrangement and receiver stationa-According to the instant invention and referring to Fig. 1 of the drawings, ;A represents a'rectangular landing field laid out to provide a series of squares B, each of which defines an area 1200 feet square. In the center of each square is a field receiver station, and these stations are designated l to 25 inclusive,l At a point approximately 1500 feet from each of the landing field boundaries (designatedN, W, S and E and corresponding to the north, west, South and east approaches to the field) is a marker station 26. Aligned with each station 26 but located a mile and a half distant, is a marker receiver station 21. The respective field and marker receiver stations each consist of an underground compartment 28 having a suitable closure 29 which is centrally formed with an antenna mounting 30 designed to vertically support an antenna 18 inches. The antenna mounting 30 and the construction of the antenna are such as to peri 3| having an electrical height of approximately mit the antenna to be deiiected on impact and wave receiver 32 connected to antenna' 3| and permanently tuned so as to respond to short wave signals transmitted at a predetermined frequency; an audio oscillator 33 adapted to oscillate at a predetermined audio frequency and which feeds into the audio frequency output lines 34 and 35 extending through one side of compartment 28, hereinafter to be referred to as the audio frequency side D of the 'receiver station; a power unit 36 connected tothe power supply lines 31 andl 38 entering the opposite side of compartment 28, hereinafter to be referred to as the power input side F of the' receiver station.

The output of power unit 36 is connected to the receiver u it 32 and to audio oscillator 33 to supply their p ate, filament and grid circuits re-- spectively. Between the receiver unit 32 and audio oscillator unit 33is an oscillator control unit 39 including a dry disk rectifier 40, an electro-magnet 4| and a circuit breaker l2 included in the output `'circuit of thepaudio oscillator, so as to'open'and close the audio frequency output circuit of the oscillator 33, whent'nerectified output of receiver 32 energizeselectro-magnet ll and loses circuit-hreaker 42 normally held in an open position by spring 43';

As the assembly C within compartment 28 is of'conventional design, it forms no part of the instant invention except in so far as itfunctions to produce, by means of oscillator 33, a signal at a desired audio frequency, when the receiver unit 32 responds to a signal transmitted. from an aircraft, hence the various units within-the compartment 28 and their electrical connections -i'iave been symbolically designated to indicate that when antenna3| has been impinged by a radio beam modulated at the frequency to which receiver unit 32 is responsive, the rectified output of the receiver unit functions to energize the electro-magnet 4| so as to close circuit-breaker Vand 44 and these are connected to bus-lines 45 and 46 which in turn are connected to bus-lines 41 and 48 connecting with lines 49 and 50 extending'to a control panel G within the control tower hereinafter to be' referred to. Likewise, the audio frequency output lines 34 and 35 on the audio frequency side D of the marker stations 26 and 21 are connected to bus-lines 41 and 48 which in turn connect with lines 49 and 50, so that the audio, frequency output of the various marker stations may be conducted to the panel in the control tower 5| via the lines 49 and 50, common to the output of both the field and the marker recelver stations, as clearly shown in Flgs; 2 and 9 of the drawings.

Although the field and marker receiver stations are structurally identical, they differ in respect to- (a) Their response, that is to say, all of the field receivers are adjusted to respond to a short wave trnsmitted at a frequency of 300,000 kilocycles per second, while all of the marker receiver stations are tuned to a frequency of '75,000 kilocycles per second, and

(b) The manner of supplying power to the:

power units 88 in compartment 28, as will be hereinafter described.

From the preceding description, it will be apparent that when the antennas of the field receiver stations are impinged bya short wave signai transmitted at a frequency of 300,000 kilocycles per second, their oscillators will be started to produce signals at audio frequencies N1---N25 for a purpose hereinafter to be descrlbed.

' Landing field control tower and transmittng equipment- At a. suitable point adjacent the landing field A is a control tower 5| the output of which, modulated at a predetermined signal frequency, is adapted to' be transmitted to a fieldv transmitter station 52, as clearly shown in Fig's. 2 and 9 of the drawings. Within control tower 5| is a distributing panel G upon which is mounted a master power supply switch H, controlling .the power supply from power mains 53 and 54 circuit and connecting the output of oscillatory unit M with the transmitting apparatus K.A

' landing field A.

The double pole power supply switch H has its terminals 55 and 56 connected to power supply mains 53 and 54, and its remaining terminals 51 and 58 connected via conductors 59 and 60 with terminals 6| and 62 of the |double pole marker power 'supply switch N, the remaining terminals of which are connected via conductors 63 and 64, 65 and 66, and 31 and 38, to the power input side F of the marker receiv-ing stations 26 and 21, located at the north approach of the -To' distribute the power supply from conductors 59 and 60 to the marker power supply switches W,'S and E, said conductors are connected witlt bus-bars 81 and 68 and to these are connected the terminals 69 and of switch W. The remaining terminals 1| and 12 of this switch are connected via. conductors 13 and 14,-

15 and 16, and 31 and 38, with the power input side F of marker receiver stations 21 and 28, on

the west approach to the landing field A.

Marker station power Vsupply switch S has its terminals 11 and 18 connected to bus-bars 61 and 68 and the remaining terminals 19 and 80,

'connected via conductors 8| and 82, 83 and 84,

and 31 and 38 with the power input. side F of the market receiver stations 28 and 21, located at the south approach to the landlng field A.

Marker station power supply switch E has its terminals 85 and 88 connected to bus-bars 61 and 68. and the remainlng terminals 85' and 88' connected via conductors 81 and 88, 89 and 90 and 31 and 38, with the power input side F of markers 26 and 21, located at the east approach of landing field A.

vWith' this circuit arrangement, it will thus be seen, assuming that switch H has been closed, power may be supplied from mains 53 and 54 through switches N, W, S, E to any selected pair of marker receiver stations, thus permitting the operator in the tower 5| to selectively determine the operation of the marker receiver stations at the north, west, south 'and east approaches to the field in accordance with the direction of the prevailing wind.

To supply power to the field receiver stations to 25 inclusive, field power switch I has its terminals 9| and 92 connected via conductors 9|' and 92', with conductors 59 and 60, and the remaining terminals 93 and94 connected via conductors 95 and 98 with conductors 91 and 98, in the landing field A. 'Conductors 91 and 98 are connected with distributing conductors 99 and |00 to which are connected conductors' 31 and'38 on the power input side F of' the various field receiver. stations, as clearly shownin Figs. 2 and 9 of ,the drawings. When the double pole switch I, has been closed, power will be supplied from 'the main's 53 and 54 through switches Hi and Iand conductors 59 and 60, 9|' and 92', and 95 and 96, field conductors 91 and 98, distributv ing conductors 99 and |00 and 'conductors 31 and 38 to all o f the receiver stations.

To informthe operator at the control tower with respect to the operation of the marker receiver stations, a signal lamp |0| is located above each of the switches N, W, S and E and connected across each of the power supply conductors 63 and 64, 13 and 14, 8| and 02, and 81 and 88 extending from said switches to the N, W, S and E marker stations, so that when any pair of these stations is in operation, the signal lamp will be lighted. Likewise, Vif desirable, a similar signal lamp' |02 may be placed across the power supply lines 95 and 98 extending from switch I to the field receiver statons, so as to ndicate that 'the fleld stations are in operative condition. To control the operation of oscillator M .and at the 'same time flash a signal when said oscillator is thecircuit of the lamp. The rem'aining terminals 106 and 101 of switch L' are included in the audio frequency output Circuit of an oscillator M, whereby when switch L has been closed the other blade v of'said'switch will close the output circuit of oscillator M. The audio frequency output circuit of 'os'cillator`M, 'graphicallydesignated by conductoi's'1091 101 and 100, is' adapted to be con- |nected to'i'the audio frequency input, conductors '110`and"111 'of the signal and speech transmit-- ting-apparatus K, as'c'learly shown in Fig. 9 of the drawings. To control the input ofv transmittingV-apparatus K, said input circuit is provided with a double throw control switch J, having its terminals 112 and 113 connected to lines 110 and 111, and. its remaining terminals l114 and 115 connected to the lines 116 and 1 1'1 entering apparatus K. `The output of apparatus K modulated at signal-frequency is adapted to be transmitted to field'transmitter 52 (via the conductors 118`and 119.

According to the panel arrangement` which has justbeen 'described' it'will be' manifest, the operator in the signal tower may control the power supply to the marker'receiver stations' and 21 sol by means of switches H, N, W, S and'E and to vall of the field receiver stations by switch I. Likewise by double .pole switch 'L, theo'utput'of 'oscillator M may be connected-to' the input of. the signal and speech transmitting apparatus K to fcause the latter to transmit sig'nals'modulated at the frequency of lthe inafter appear.

`A'power unit 120 is connected with the power supply lines .59 and 60 via conductors 121 and t 122 and with (the oscillator M, signal and speech transmitting apparatus K, via the conductors 123 and 124, and' 125 and 126 to supply'the plate, vfilament and grid circuits of the oscillatorvand trans- .mitting apparatus K, as will be'understood'without further discussion.

.the drawings. .As these terminals 121 and 128 are also'connected with conductors 110 and 1 H of the transmittingv apparatus K, it will be apparent that s'ignals coming into the control tower from the field will be transmitted viav conductors 110 and 111, switch J and'conductors 116 and 11'1 to' transmitting apparatus K, andv will modulate the lthe fre-` quency of the incoming signal, as will be'readily output of the transmitting' apparatus at understood withoutfurther discussion.4

Inasmuoh as the power unit 120., osoinator M and transmitting'apparatus K are of conventional design and form no part of the present invention, except in ,so far as they serve to .produce oscillations of `Y'a predetermined frequency and to transmit the signals entering the tower from the field, said power'unit os'cillatcrM, trans-- mitting apparatus oscillator M for a purpose to here- To transmit theaudio frequency `sig nals from' vthe marker and the field receiver fsftatio'ns to the. transmitting -apparatus K within the 'control V towerrthe audio frequency output conductors 49 i K and their associated input acoziac a short wave transmitter unit 132,' the latter being' adapted to transmit at a frequency of 300,000 kilocycles per second. The design of radiator i3i is such as to project a radio beam in the direction of the line ofrfiight, the beam having a radiation pattern conforming to that shown in Fig. 1 of the drawings. At a distance of a mile and a half from the field boundaries and at an altitude of 800- feet, the spread of this beam will correspond' to the width of the landingfield, which in the present instance is 6,000 feet, as shown in Fig. 1 of the drawings. 'This beam constitutes what hereinafter will be referred to as the landing beam B.

Arranged in the bottom of the airplane in suitably spaced relation are two radiators 133 and 630. These radiators are positioned so as to project their beam in a direc'tion normal to the line 'of flight and are connected to short wave transmitter units and E35 respectively. Transmitter unit 135 connected with radiator 133 is adapted to transmit at a frequency of 75,000 kilocycles per second. The design of radiator 133 is-such as to project a short wave radio beam having a radiation pattern which' at an altitude of 800`feet will be wide enough to extend across'the field, that is to say, the spread of the beam at the height mentioned, will 'cover an'area 6,000 feet wide, as shown in 'Figz 4 of the drawings. This 'beam hereinafter will be referred to as a marlrer station beam R.

The transmitter unit E36 connected with radiator 134 transmits at a frequency of 300,000 kilocycles per second and its-radiator is equipped with a lparabolic reflector so as'to project a short i wave radio beam having a conical radiation pattern, hence when the plane is at an altitude of 800 feet, the beam will cover substantially one v of the s'quar'es of the landing field, as elearly shown in Fig. 3 of 'the drawings. This beam hereinafter'will be referred to as the' field receiver station beam T. I

The three short wave transmitter 'units 132,

' 135 and`136 -are adapted to' be modulated b'y a The' operation of these units andof the modula'tor is adapted to be Controlled by switches'138 and 14'3' included in' the circuits represented by conductors 139 and single modulator unit 131.

140, extending from switch 130'; conductors 141 and v142 connected with the modulator and extending fromconductors 139 and to modulator 131; co'nductors 143 and 144 extending from conductors 139 and 140 to transmitter-unit 132; conductors 145 and 146 extendingl from conductors 139 and 140, to transmitter unit 136, and conductors 148 and 141 extending fror'n conductors 139 and- 140 to transmitter unit 135. These connections are such that when switch 138 fhas .been closed, 'the two transmitters 135 and 136 and modulator unit 131 will be operated to project the beams R. and T; Switch 143' enabes separate operation of transmitter unit 132 and the projection of beam'P As the modulator and transmitter units just mentioned, are of conventional design and hence form no part of the instant invention, except in so far as they function to provide the short wave beams P, R and T, these units and their connections have been symbolically shown in Fig. 7 of the drawings.

With the three transmitters and their radiators arranged on the aircraft as shown in Figs. 6 and 7, it will be seen that when switch 138 has been closed radiator 133 will project a marker station beam R normal to the line of flight and at a frequency of 75,000 kilocycles per second; radiator |34 will project a beam T, likewise normal to the line of fiight and at a frequency of 300,000 kilocycles per second. When switch M3' has been closed radiator |3| will project a beam P in the direction of the line of fiight and at a frequency of 300,000 kilocycles per second.

These three beams P, R. and T are adapted to control the operation of the field and marker receiver stations hereinbefore described.

Position ndcator.-Mounted on the instrument board of the aircraft in view of the pilot is a position indicator U having a rotatable finder A' adapted to be oriented with respect to the landing field A and the indications of the compass X. The rotary movement of finder A' is effected by a remote control device V mounted on the steeringwheel or other convenient part of the aircra'ft. Indicator U is electrically connected by cable U' with a selector mechanism Y which latter is controlled by and connected with the audio frequency output of a conventional receiver Z suitably located aboard the aircraft, as shown in Fig. 8 of the drawings.

Indicator U comprises an outer cylindrical housing vlll adapted jto be fitted into a suitably dimensioned opening in the instrument board. Housing ISO is formed With a cylindrical extension |5| interiorly provided with aligned bearing openings |52 and 153l adapted to suitably journal shaft li supporting an inner annular casing i55, positioned within the housing. Casing |55 is adapted to be closed by a translucent glass panel I 56 held in position by a metal retainer ring' |5`i', as clearly shown in Fig. 11 of the drawings.

Interiorly, the inner casing |55 is divided by the intersecting partitions 058 into a series' of square compartments lnumbered lc to 25a inclusive. In addition to the squares la to 25a inclusive, partitions I58' provide a plurality of segmentally shaped compartments 26a and 21a extending around the area occupied by the squares' as clearly shown in Fig. 12 of the drawings. In each of the squares la to 25a inclusive, is an incandescent lamp,l the lamps in the various squares being numbered lb to 25h inclusive. In each of the four segmentally shaped compart'- ments is an-incandescent lamp and these are designated 26h and 21h respeotively.

When viewed through translucent panel I 56 the edges of partitions |58' and 158 underlying the panel |56, outline a plurality of segmentally shaped portions 26a and 210 (Fig. which surround a rectangular area divided into a series of squares numbered lc to 25a inclusive (Fig. 10), thus providing a finder A' affording a facsimile of the squares on the landing field containin'g the field receiver stations hereinbefore identified as I to 25 inclusive.

The segmental portions designated 260 and 210 of the finder A' extending around the rectangular area, are colored green and that is to say, the segmental portions of the blue respectively,

finder overlying the similarly shaped compartments 21a are colored blue and those overlying compartments 26a are colored green, as clearly shown in Fig. 10 of the drawings. With this arrangement a white light will be fiashed in each of the squares ic to 250 inclusive, representing the field receiver stations I to 25, a blue light for each of the segments 210 indicating the 1500 marker receiver stations 26, and a green light for each of the segments 28a, indicating the mile and a half marker receiver stations 21.

To energize the incandescent lamps lb to 25h inclusive, one side of each of said lamps is connected via conductors ld to 25d inclusive, with commutator rings le to 258 inclusive, mounted on shaft 054. The other side of these lamps (lb to 25h inclusive) is connected to ground via the five distributing conductors |59, |60, |6l, l62 and 163, common return conductor l64, commutator ring |64' .on shaft l54, brush 165 and ground 166, as clearly shown in Figs. 11 and 12 of the drawings. Likewise one side of each of the incandescent lamps Zlb in segmental' compartments 21a is connected via the four branch conductors 2'ld and the distributing conductor 218 with commutator ring 2l on shaft |54. The remaining side of each of the incandescent lamps 21h is connected to ground via the four branch conductors 21g, the distributing conductors i62 and |63, common return conductor IM, brush l65 and ground |66. Also one side of each of the incandescent lamps 26D is connected via conductors 26d and distributing conductor 268 with a commutator ring 26 on shaft |5ll. The remaining side of each of the lamps 26h is connected via conductors 26g and distributing conductors |;B0 and |63 with the common return conductor IW. and thence to commutator ring IW', brush |65 and ground N56.

It will thus be seen that one side of all of the incandescent lamps in casing 155 is connectedl to the commutator rings on shaft l while the other' side of all of said lamps is grounded through the common return lead M54, brush |65 and the ground ISS. i

Mounted on the instrument board of .the aircraft adjacent the position indicator A is an auxiliary signal lamp I 61, the purpose of which will be hereinafter set forth. To energize this lamp I 61 one side thereof is connected via 'terminals I 68' and G69 with ground 'brush |65 and the remaining side is connected with conductor |10 which connects with armature switch I'H in the selector mechanism hereinafter to be described.

To enable the finder A' to be rotated, shaft |54, (Fig. 11), is provided with a ring gear 113 adapted to mesh with the bevel gear IH suitably journaled in bearings 115. Gear |14 is connected to a Cardan cable 116 which extends to the housing' ITB of the control device V mounted on the steering wheel, as shown in Fig. 8 of the drawings. The free end of the cable 115 terminating in housing |18 is provided with a gear (not shown) adapted to mesh with a suitably arranged gear (not shown) controlled by the operating 'knob 119, of control device V, so that as said knob |19 is operated shaft |54 of inner casing 155 will be rotated, thus permitting orientation of the finder A' with reference to the landing field, as will be understood without further discussion.

To distribute electrical energy to the commutator ringsA and from the latter to the various incandescent lamps in casing |55 numbered la to 25a inclusive, cylindrical extension |5l is provided with a series of brushes numbered l to inclusive, which are adapted to contact with the commutator rings numbered ie to 25e inclusive. Brushes l to 25)* inclusive are each connected to conductors designated lg to 25g inclusive, the free ends of which-are connected to armature switches designated lh to 25h inclusive, which are located in the selector mechanism, hereinafter to be described. The commutator rings Z'land 26 coact with brushes 2'lg and 26g likewise mounted in the cylindrical portion ll of casing ISB. 'Brushes 21g and 26g are connected to conductors 21h, and 26h, the free ends of which are. connected with` armature' switches 2h and 26i in the selector mechanism, hereinafter to be described. 'I'he several conductors lg to 25g and 21h and 26h inclusive,

I are enclosed in a suitable casing U', which extends from the position indicator to the selector mechanim. It will thus be apparent that the electrical energy brought to the brushes will be transmitted through the latter to the commutator rings and from the rings through the various incandescent lamps to the common return conductor E64 and thence through brush IBE to ground E56. w

Selecior mechansm.-Within the casing enclosing the selector mechanism Y are arranged (Fig. 12) twenty-eight A. C. relays disposed in groups numbered li' to 251' and 213i, 257' and I'Hy'. The respective relays are positioned so as to coact with armature'switches lh to 25h, 212', 26i

and HH, whereby energization of the relays will cause the armature switches to engage their complemental stationary contacts numbered Ii to 257' and 21k, 26k and l'llk, as clearly shown in Fig. 12 ofthe drawings.

To conduct electrical energy 'from the positive side of battery-980 to the several contacts above mentioned, stationary contacts I'j to 57'l are connected to branch conductor l8l; contacts Bit to E07' to branch conductor i82; contacts U7' to lzi to branch conductor |83; contacts |6; to 2107' .to branch conductor IM; contacts 2h' to 257' to branch conductor l85; contacts 21k, 26k and i'Hk to branch conductor |80.` These branch conductors 88| to 186 inclusive are connected to distributing conductor l81 extending from the positive side of a battery l80, the lnegative side of which is grounded at |89,'as clearly shown in Fig. 12 of the drawings.

By virtue of these connections, when the respective armature switches lh to 25h, 261', 2111 and I'llz' 'have been brought into engagement with their complemental stationary contactsla" to 257', 26k, 21k and I'llk, electrical energy will be permitted to flow from' the positive side of battery |89 through distributing conductor |8'l' to the branch conductors |8| to l86 and from these conductors to the stationary contacts |:i to 257', 26k, 21k and 'Hk, armature switches Ih to 25h, 261, l2112 and' I'lfi, and conductors lg to 25g, 2th.,v 26h, tov the brushes mounted on the position indicator U and to one side of signal lamp |6`l via conductor l'l0 for a purpose hereinafter to be described.

To energize the various relays, each of which:

is responsive to a different audio frequency,

` said relays are connected to the output side of a lconventional radio receiver Z, located aboard the aircraft and in a position where it may be readily. tuned by 'the pilot. This connection is effected as follows:

Relays li to 5a' are connected to branch con-v ductors l90 and |9l; relays-62' to 101' to branch conductors l92 and E93; relays Hi to Ii to branch conductors '894 and ISS; relays |6i to y20i to branch conductors ISB and l9'l;. relays 2612 to 252' to branch conductors |98 and |99; relays 'lj, 2M and i'li to branch conductors 200 and 2M. The branch conductors l90 to 20| inclusive are connected to the distributing conductors 204 and 205 extending from 'the audio frequency output side of the receiver Z, whereupon the output of receiver Z at audio frequencies N1 to INza will be distributed to the various relays to effect their selective operation, as will hereinafter appear.

According to the preceding circuit arrangement, reception of a signal by the receiver Z Vmodulated at audio frequency N1 will produce currents in the output distributing leads 204 and 205 of the receiver 'at the audio frequency N1 and these currents will 'flow through .all of the A. C. relays .but will effect only the relay respon-- sive to audio frequency N1, namely relay li.

Energization of relay li will cause said relay to attract its armature lh andv cause the latter to engage the complemental stationary contact la', thus permitting current to flow from battery through conductor |8'l to armature switch 'area lc on the finder or screen A'. In like manner audio frequencies N2 to N25 will cause the incandescent lamps 2b to 25h to be lighted and the areas 2c to 25c on findervA' to be illuminated as will be understood without further discussion. Similarly a radio -signal at audio frequency Nza will energize A. C. relay 267' to attract armature 202' of this relay and complete the circuit from i battery |80, distributing conductor l8v'l, branch conductor |86, stationary contact-26k, armatura switch 2M, conductor 26h, brush 26g, commutator ring 26, conductor 268, branch conductors 26d to one side of the four incandescent lamps 28h in'the compartments 26a. From the other side of the four lamps '26h ,the current will flow through the branch conductors 26g to the common return conductor IN, commutator ring lflr', and thence to brush |65 and ground I 66, to illuminate the four segmentall'y shaped green areas 260 on the finder a' representing the 1500 foot marker receiver -stations. In like manner reception of a signal at audio' frequency N'M will energizethe A. C. relay 217' and complete the' circuit of battery |80, through the four incandes- Q0 cent lamps 21h to illuminate the four segmentally shaped blue areas 2'lc of thefinderA A', representing the one and a half mile marker receiver stations'. 1

In order to afford an auxiliary danger signal' for the pilot of the aircraft there is provided the signal lamp |6'I controlled by the relay lllzi which is responsive to signals modulated at audio frequency N28. .When energized by currents at audio. frequency N88, relay l'll' will Aattract armature l'll and close the circuit from battery |80 to vone side of signal lamp |6'l.via conductors.

|8'l, |86, stationary contact-Il l'k, armature switch "In, conductor I'IO, signal lamp IS'I 'and from the other Side .of signal lamp IH' to ground ISB liftV via conductor i69, thus completing the circuit of said lamp |6l' and causing its illumination.

Operation.- Having described the structural' and electrical details of tion is as follows:

Assuming that an aircraft, fiying at an altitude of 800 feet, is coming into landing field A;

this invention, its operathat radio receiver Z, aboard the aircraft has been tuned to the signal frequency of field transmitter 52 and that beams R and 'I' (Fig. 6) are emanating from radiators |33 and |3ll which latter are in electrical relation with short wave transmitters i 35 and |36, adapted to transmit at the frequencies of 75,000 and 300,000 kilocycles respectively, and further assuming that with the aid of directional signals from the operator in signal tower 5|V the aircraft has been flown across the field as it is located above receiver station |3 with beam T directed upon said station, as shown in Fig. 3 of the drawings.

Aircraft O being disposed above station |3, as in Fig. 3, radiant energy from beam T will excite antenna 3| of receiver 32 (Fig. 2), and since the latter is tuned to the frequency of beam T. high frequency currents will be set up in the receiver output circuit and these currents after rectification by rectifier 60, will energize relay and actuate switch 62 to close the audio frequency output circuit of local os'cillator 33, whereupon signals at audio frequency N13 produced by oscillator 33 will fiow over conductors 30 and 35 (extending from the audio frequency side C of compartment 20 to conduetors 43-40, fl 06, iii- 68,

00-50 to the audio frequency input vterminale i 21| and |28 of panel G located in control tower From terminals |2`| and |28 the signals will flow over conductors ||0 and HI, switch J, conductors M6 and into the signal and speech transmitting apparatus K, whereupon .w signals at the signal frequency of the field transmitter 52but modulated at audio frequency N13 will be transmitted from field transmitter 52, as will be understood without further discussion..

As the signals emanating from field transmitter 52 are picked up bv receiver Z aboard the aircraft (Figs. 8 and 12). currents lwill be caused to flow in the output circuit of said receiver Z which includes audio frequency distributing leads 204 and 205, branch conductors |90 to 20| inclusive, and A. C. relays ii to 252'. 267'. 2`|7` and l'llj of selector mechanism Y. None of the A. C. relays however, will be aifected with exception 'of relay |3i which as hereinbefore stated, is responsive to signals at audio frequency N13. When relay |3 has been energized. its armature switch I 3h will be actuated to close a lamp circuit which extends from the positive pole of battery |80 to one side of incandescent lamp 3b. located in compartment i 3a of the position indicator U and from the opposite side of said lamp |3b to ground |66 and from said ground to the grounded side of battery |80, (Fig. 12) thus completing the circuit of lamp |3b and illuminating the square |3c representing the field receiver station 3 on landing'field A. Illumination of square |3c on the finder or screen A' informs the pilot that his aircraft is above square |3 on the landing field, as shown in Fig. 3.

As the aircraft without change of course, continues'its flight across the landing field toward, let it be assumed, the north boundary, the radiant energy of beam T'will successively excite the' antennas 3| of field receiver stations 8 and 3, so that signals at the frequencies NB-N3 of the local oscillators 33, associated with these stations, will be fed into the signal and speech transmitting apparatus K at the control tower so as to effect modulation of audio frequency NH- N-f of .the signals transmitted from apparatus K, via conductors HB and |99'to the radiator system of the field transmitter 52. As the signals from field transmitter 52 modulated at audio frequencies Ni--N3 are picked up by the receiver Z aboard the aircraft, currents will be set up in the audio frequency output reads 204 and 205, (Fig. 12), of said receiver Z and from leads 204 and 205 these currents will flow to the A. C. relays of selector mechanism Y to energize relays 8:' and 3z' responsive to frequencies N8-N3. When relays 82' and 31' have been energized, the circuit of battery |80 will be closed through the incandescent lamps 8b and 3b' located' in position indicator U, to light said lamps and illuminate squares 8c and 3c of the finder or -screen A', thereby indicating to the pilot that the .aircraft has successively passed over squares 8 and 3 on the landing field, as will be understood without further discussion.

After proceeding back and forth across the landing field several times to definitcly locate the position of the aircraft relative to the various field receiver stations, let it be assumed that the pilot again heads the aircraft towards the north boundary. Upon passing this boundary and reaching al point 1500 feet therefrom radio beam R (the width of which corresponds' to that of the landing field) (Figs. 04 and 5), will be directed upon marker receiver station 26.

The antenna 3| of station 26 'when excited by the radiant energy of beam R will, as in the case of the stations previously roferred to effect transmission of signals from the field transmitter 52 'at audio frequency moduation N26. When signals modulated at the frequency N26 are picked up by receiver Z aboard the aircraft, the currents set up in the output circuit of the receiver will be `distributed to the A; C. relays in the selector mechanism Y to energize relay 261` actuate its' armature 262' and complete the circuits of the four lamps 26b in the position indicator U, to light said lamps and illuminate the segmentally shaped green areas 26a of the finder A', thus informing the pilot that the aircraft is directly over marker station 26, located at a point 1500 feet from the north boundary of the landing field.

Without change of course, the ship is fiown to a point situated a mile and a half from marker receiver station 26 and at this point the beam R impinging antenna 3| of marker station 2`| will excite said antenna and thereby cause the field transmitter 52 to transmit signals modulated at audio frequency N27. As signals at this frequency are received by receiver Z aboard the aircraft, they will energize relay 217' and close the circuit of battery i 80 through the four incandescent lamps 2`|b of the position indicator U to light said lamps and illuminatc the four segmentally shaped blue areas 210 to indicate to the pilot that the aircraft is located above the mile and a half marker station 21. When these blue signals have been received by the pilot, the aircraft is caused to describe a 180 turn so that it will be 'headed back toward the north boundary, as shown in Figure 1 of the drawings., At the lsame time the pilot switches on the short wave transmitter |32 Operating at a frequency of 300.000 kilocycles and projecting the beam P in the direction of the line pf night.

' one or two stations, which will be indicated by angle and headed back toward the continuous illumination of the corresponding areas on the finder A', as will be understood Without further discussion. Hence the pilot by directing the flight of the aircraft so that the beam continues to play on a selected station, establishes a landing beam by which the aircraft may be brought to a safe landing at known points on the field. i

From the preceding discussion of the operation of the instant invention, it will 'be evidentwhen the aircrait O is above any of the field stations i to 25 inclusive, 'the corresponding square of those designated lc to 250 on the screen A' of the position indicator U, aboard the aircraft will be illuminated. When the'- aircraft passes above the field marker station 26 located at a point 1500 feet from the field boundary, the four segmentally shaped green areas of thel finder` A will be illuminated and as the aircraft passes the field marker station located a mile and a half from the 1506 foot marker station, the four segmentally shaped blue areas 216 of finder A' Will be illuminated to inform the pilot that at this point the plane should be turned through a 1800 the landing field preparatory to making a landing along the landing beam P radiating from the aircraft in the direction of its line of flight.

Conditions may arise when it would be extremely dangerous for the pilot to make a landing, as for instance, inundation of the landing 'field by a recent fiood. In this event, in order to warn the pilot of the aircraft regarding the' dangerous condition of the field, a danger signal lamp ifi'l, mounted on the instrument board is illuminate'd. Assuming the hazardous field condition mentioned, 'the operator in the signal tower closes the switch L `on panel G (Fig. 9) and completes the output circuit of oscillator M, so as to transmit signals from its output circuit at the frequency N28. As the -output of the oscillator M is' connected via conductors |08 and 899 (Fig. 9), to conductors HO, said signals will flow from'the conductors |08, HIS, HU and HI to i' switch J, and through said switch via conductors HG and IH to the signal and speech apparatus K whereby the signals will be transmitted at a frequency of N28.

The signals transmitted at frequency N28 When picked up by receiver Z aboard the ai'rcraft will be transmitted via the conductors 204 and 205 to the various A. C`. relays in the selector mechanism Y, whereupon relay .Ill will be energized to attract its armatura |1|i and complete the circuit from battery l80 to one side of signal lamp lfi'l via conductors IB'I, |86, contact I'Illk, armature ilii and conductorl'l. From the other side of signal lamp 161 the current will flow. via conductor IGS to ground |66, thus completing the circuit through lamp4 IB'I to light said lamp and warn the pilot that conditions on the field preclude a sife landing.

In conclusion, it will be apparent that when the landing field and the aircraft have been equipped as hereinabove stated, it is possible for the pilot of an air-Craft to -be guided solely by the indications on the position indicator U aboard the aircraft in definitely locating the position of aaoaeas said aircraft with reference to one or more field stations on the landing field and to select a particular station for the purpose of making a landing and to make this selection without regard to atmospheric or other conditions which heretoforev have made landing, under conditions of poor or of no visibility, extremely hazardous.

Having described my invention, what I 'claim and wish to secure by Letters Patent is:

1. A navigational' guide system comprising a landing field laid out in a series of geographic divisions, a field receiver station located in each division, each' receiver station including a signal rece'iving device responsive to a predetermined frequency, and a local audio frequency oscillating unit adapted to oscillate at a certain audio frequency value and to be-set in operation by said device, a field transmitter adapted to transmit at a predetermined carrier frequency, means in electrical relation with the field receiver stations and with said field transmitter to modulate the carrier frequency of the'latter at different audio frequency values, determined by the audio frequency output of the local oscillator unit associated with each of said receiver stations, an aircraft, means aboard the aircraft for transmitting a radio beam normal to the line of flight of the aircraft, said beam having a signal frequency corresponding to that to which said signal receiving devices are responsive whereby as the aircraft crosses said landing field the beam will successiveiy sweep the divisions thereof, and energize the receiver station in each division, a signal receiving system aboard the aircraft including means for receiving the signals transmitted from the field transmitter and means for translating the audio frequency values of said signals into visual. signals aboard the aircraft,

indicating the particular receiver station upon a field transmitter adapted to transmitat a predetermined carrier frequency, means in electrical relation with the field receiver stations and with the field transmitter to modulate the carrier frequency of the latter at different audio'frequency values, determined by the audio frequency oscillating units at each of saidreceiver stations, an aircraft, means aboard the aircraft for transmitting a ,radio beam having a conical radiation pattern whereby when said aircraft'is at a predetermined altitude and immediately above a receiver station, the spread of the beam will be such as to cover but one of the squares of saidA landing field, said beam having a signal, frequency corresponding to that to which the field receiver stations are responsive, and being directed normal to the line of flight of said air- 'craft whereby as the latter crossessaid landing field the beam will-successively cover each square thereon to energize its receiver statioma signal.

receiving ,system aboard. the' aircraft including means'for receiving signals fromthe field transmitter and means for. transmitting thev audio frequency values of saidsignals to produce visual signals aboard the aircraft indicating the particular receiver station upon which the beam from the aircraft is directed at the time the vvisual signal is received.

3. A navigational guide system comprising. a

" landing field laid out in a series of squares of i device, a field transmitter adapted to transmit -at a predetermined carrier frequency, means in electrical relation with the field receiver stations and with said field transmitter to modulate the carrier frequency of the latter at different audio frequency values, 'determined by the audio frequency oscillating units of each of said receiver stations, an'aircraft, means aboard the aircraft for transmitting a radio beam having a radiation pattern whereby when said aircraft is at predetermined altitude and immediately above a receiver station the spread of said beam Will'be such as to cover but one of the squares of said landing. field, said beam having a frequency corresponding to that to which the field receiver stations are responsive and being directed `normal to the line of fiight of said aircraft, whereby as the latter crosses said landing field the 'beam will successively cover each division to energi'ze its receiver station, a signal receiving system aboard the aircraft including a receiver for receiving the signals transmitted from the field transmitter, said receiver embodying an output circuit, and a position indicator in the output circuit of said receiver, said position indicator including a translucent screen laid out in a series of squares corresponding to those of thelandingv` 'field, an illuminating device in connection with each square of said screen and selectively responsive to the audio frequency. values of the .signals transmitted over the ouput circuit of said receiver to illuminate a selected square on the screen corresponding to the squares of the landing field upon which the radio beacon of the aircraft is directed at the time the visual signal is received.

4. A navigational guide system comprising a landing field laid out in a series of squares of predetermined dimensions, a field receiver station arranged in each square, each of said receiver stations including a signal receiving device respnsive to a predetermined frequency, and a local audio frequency oscillator unit adapted to oscillate at a certain audio frequency value and to be set in operation by said device, a field transmitter adapted to transmit at a predetermined carrier frequency, means in electrical relation withthe field receiver stations and with said transmitter to modulate the carrier frequency of the latter at different audio frequency values, determined by the audio frequency oscillating units' of each of said receiver stations, an aircraft, means aboard the aircraft for transmitting a radio beam having a conical radiation pattern whereby when said aircraft is at aA predetermined altitude and immediately above a receiver station, vthe spread of said beam will be such as to cover but one of the squares of said landing field, said beam having a frequency corresponding tovthat to which the field receiver stations are responsive and being directed normal to the line of fiight of said aircraft, whereby as the latter crosses said landing field the beam will successively sweep each of its squares to energize the receiver stations, a signal receiving system aboard the aircraft including a receiver for receiving the signals transmitted from the field transmitter, said receiver having an output circuit, a position indicator, said position indicator including a 'rotatable translucent screen I adapted to -be oriented with respect to the landing ,field, said screen being divided into a series of squares corresponding in number to those of .tion centrally located in each square, a field marker station exterior of each of the landing field boundaries and at a predetermined point with respect thereto, each of said field receiver stations and said marker stations including a signal receiving device responsive to signals of a predetermined frequency, and a local audio frequency oscillating unit adapted to oscillate at a certain audio frequency value and to be operated by the response of the signal receiving device, a field transmitter adapted to transmit at a predetermined carrier frequency, means in electrical relation with the field receiver stations, -the field marker stations and the field transmitter to modulate the carrier frequency of the latter at different audio `frequency values,

determined by the audio frequency oscillatingquency corresponding to. that to which the receiver stations are responsive, the other beam having a frequency corresponding to that to which the marker stations are responsive, whereby as said aircraft crosses said landing field the beams Will successively sweep the squares thereof to successively energize said receiver andrsaid marker stations, a signal receiving system aboard the aircraft, including means for receiving the signals transmitted from the field transmitter and means for translating the audio frequency values of said signals into visual signals aboard the aircraft indicating the particular field receiver station or marker receiver station upon which the beams of the aircraft are directed at the time the visual'signal is received aboard' the aircraft.

6. A navigational guide system comprising a landing'field laid out inl a series of squares of predetermined dimensions, a ,field receiver station centrally located. in each square, a field marker station situated exterior of each of the landing field boundaries and at a predetermined audio frequency oscillating unit adapted to oscillate at a certain audio frequency value and to` 'be operated by the response of the signal receiving device, a field transmitter adapted to transmit at a predetermined carrier frequency, means 4 in electrical relation with the field receiver stations, the field marker stations and the field transmitter' to modulate the carrier frequency of the latter at different audio frequency values,'

determined by the audio frequency oscillating units of 'the receiver and Inarker` stations, anV

aircraft, means aboard the aircraft for transmitting radio beams normal to its line of fiight, one of said beams having a frequency correspondlng to that to which the receiver stations are responsive, the other of the beams having a frequency vcorresponding to that to which the 'marker stations are responsive, whereby as said aircraft crosses said landing' field the beams will successively-sweep the squares thereof and successively energize said receiver and said marker stations, a signal receiving system aboad the aircraft including means for receiving the signals transmitted from the field transmitter and means for translating the audio frequency values of said signals into visual signals aboard the aircraft in-. dicating the particular field receiver stationor marker receiver station, upon which the beams of the aulrcraftv are directed at the time the visual signal is received aboard the aircraft, said translating means including a receiver for receiving signals transmitted from the vfield transmitter,

:said receiver having an output circuit, a\position indicator included in the output circuit'of said receiver, said position indicator including a'rotatable translucent screen adapted to be oriented-with respect to the landing field and laid wout in a series of squares to provide a facsimile of the landing field illuminating devices to the rear of the screen andin connection with each of its squares,said devices being selectively responsive to the difi'erent audio frequencyvvalues transmitted over the ouputV clrcuit of said receiver, whereby to illuminate a square on the screen corresponding to the square on the landing field upon which the beams of said aircraft are directed at the time the signal is received aboard the aircraft.

'LA navigational guide system comprising a landing field laid out in aseries ofl squares of predetermined dimensions, a field receiver station arranged in each square, a pair of marker stations situated exterior of and in predetermined spaced relation With respect to each. other and to each of the boundary lines of said landing field, said field receiverstations and said marker stations including a signal receiving device responsive to a predeterminecl` frequency, and a' local audio frequency oscillator unit adapted to' oscillate at'a' certain audio frequency value and to be operated by the response of said signal receiving device, a field transmitter adapted to transmit at a predetermined carrier frequency,

means in electrical relation with the 4field recei'ver' stations, the field marker stations and the field transmitter to mo'dulatethe carrier frequency of the latter at different audio frequency values determined by the audio frequency oscillator units of the field receiver and marker stations, an aircraft, means aboard 'the aircraft 'for transmitting la pair of radio beams normal to the line of flight of said aircraft, one of said beams *having a radiationI pattern, the' spread of which is coextensivewith the width of the field when the aircraft is. disposed .at arpredetermined altii tude with respect to said field, the. other ofr said` beams ,having a 'conical-V radiation pattern, -the spread of -whichl-when the air-craft at :a certainaltitude will be such as to cover but one 'of 'the aaoaeae squares of said field, one of said beamsv corresponding in frequency. to ythatv to which the field receiver stations have been tuned, the other of said beams having a frequency corresponding to that to which the marker stations have been tuned, whereby as said aircraft crosses said landing field at a predet'ermined valtitude, said field marker station, illurninating devices in,

connection with the squares and segmentally shaped areas of said screen, said .illuminating devices being selectively Controlled by the diffferent audio 'frequency values generated in the output circuit of said receiver, whereby to selectively illuminate the squares and said .segmentally shaped areas of said screen when the beams from said aircraft are directed upon the field receiver or field marker stations.

v3. A method of transmitting and translating directive radio beacon4 signals, consisting ln sweeping a landing field with a beam of radiant.

energy emanating from an aircraft `and directed in a plane normal to its line of fiight, utllizing the sweep of the beam across the surface of the landing field to impinge a series of beam responsive points within the boundaries of the field, causing the impi'ngement of. the beam with the points to produce -a plurality of signals, each signal having a predetermlned frequency to identify.. geographicallyl the particular point 1mpinged' by the beam and then employing said signals to visuallze the beam responsive pointsv aboard an aircraft whereby to indicate the position of the aircraft relative to the respective points at'the time each visualization is received.

9. A method of transmitting and translating directive radio beacon signals, consisting in sweeping a landing field with a beam of radiant energy emanating from an aircraft and directed' in',a .plane normal to the line of iiight, utilizing the sweep of the beam across the surface of the z landing field to successively impinge a series of beam responsive points within the boundaries of the field, causing the impingement of the beam with the points to produce a series of slgnals, each signal having a different frequency to identify geographically the point impinged by, the beam and then 'employing said signals to visualize. successsively'the beam responsive points aboard an aircraft whereby to indicate the positionof the aircraft relative to the respectiveV points at the time each visualization is received.

1'0. A method of transmitting and translating directive ,radio beacon signals, consisting in sweeping a landing field with a beam of radiant energy emanating from an aircraft, the beam having a characterlstic pattern and being directed in a plane normal to its line of flight, utilizingth-e sweep and pattem of'the beam to imninge selectively a series of beam respi'msive`` points within the houndaries of the landing field, causing the limpingement of the beam with the points to produce a series of signals, each signal having a different frequency to identify geoutilizing the sweep and pattern of the beam across the surface of the landing field to impinge selectively a series of beam responsive points within the boundariesV of the field, causing the impingement of the beam with the points to produce a series of signals, each signal having a different frequency to identify geographically the point impinged by the beam and then employing said signals to visualize successively the beam responsive points aboard an aircraft.

whereby to indicate the position of the aircraft relative to the respective points at the time each visualization is received.

12. A method of transmitting and translating directive radio beacon signals, consisting inv sweeping the landing field with a pair'of radiant energy beams emanating from an aircraft and directed normal to its line of fiight, utilizing the sweep of the beams across the surface of the landing field to impinge a series of beam responsive points within and without the boundaries of the landing field, causing the impingement of the beam with the points'to produce a series of signals, each signal having a different frequency to identify the location of the point with reference to the boundaries of the field and thenemploying the signals to visualize the beam re-V sponsive points aboard an aircraft whereby to indicate the position of the aircraft relative to the respective points at the time each visualize,- tion is received.

13. A method of making a blind landing consisting in directing a beam of radiant energy from an aircraft and in the direction `of its line of flight, flying the aircraft to a predetermined position with reference to the boundary line of a fiying field, indicating said position in color aboard the aircraft, heading the aircraft toward the landing field so as to direct its beam upon a series of beam responsive points within the boundaries of the landing field to produce a plurality of signals, each signal having a different frequency to identify the position of the points with reference to said boundaries,-employing the signals to visualize the points aboard an aircraft and while maintaining visualization of the points, directing the'aircraft along the beam to the visualized points on the landing field.

14. A navigational guide system comprising a landing field laid out in a series of geographic divisions, an element responsive to radiant'en- ,ergy of a predetermined frequency and located in each divisipn, a generator for producing alternating current of a. predetermined -frequency associated with each of said radiant energy responsive elements and operable by the response of said element, said generators producing currents of different frequencies, a field transmitter in electrical relation with the respective generator and adapted to transmit the signals produced by said generators, an aircraft, means for transmitting a radio beacon from the aircraft, said beacon having a frequency within the resonant response of said radiant energy responsive elements, means in connections with the aircraft transmitter for directing the radio beacon in a plane normal to the line of .fiight of the aircraft, whereby as the latter crosses said landing field the beam will successively sweep the geographic 'divisions thereof and energize the radiant energy responsive element in each of said divisions, a signal receiv'ing system aboard the aircraft including means for receiving the signals transmitted by the field transmitter and means .for translating 'the values of said signals to produce visualzsignals aboard the aircraft indicating the particular radiant energy responsive element upon which the beacon from the aircraft is directed at the time the visual signal' is produced aboard said gg aircraft.

EDWARD M. SORENSEN. 

